Soil Mantle: The Basic Life Support System

Soil mantle of Earth is a fairly loose material, half made up of tiny particles and the other half of water (moisture) and air. This thin layer covering the planet’s land surface is the biospheres’ foundation, our primary resource and basic life support system where human civilisation has been growing its food since time immemorial. Soil is, basically, a disintegrated product of geo-chemical and biological materials of the earth over a long period of time-often thousands of years. It is an assembly of inorganic constituents derived originally from rock, which, being weathered by rainwater, atmospheric gases, ice and plant roots, has slowly broken down into loose structure called loam. Loam is a naturally fertile soil, consisting of masses of particles from clays, through silts, to sands interspersed with pores, cracks and crevices.

All good soils support life in myriad forms, which in turn supports the green mantle (forests and bushes) of earth. One hectare of good quality soil in a temperate zone may contain 300 million organisms-mites, insects, worms and other mini creatures. The soil of the tropical zone contains even much greater number of life forms with greater diversity. As for microorganisms, a mere 30 grams of soil may contain one million bacteria of just one type, as well as one lac yeast cells and fifty thousand bits of fungus. As such, the soil can be said to be an ecosystem in itself-or rather made of many ecosystems.

The process of soil formation is slow-often in decades and centuries, but it can be degraded in a fraction of the time it takes to form. At best, even when sediments build up quickly, formation of 30 centimeters of soil may take fifty long years. More usually, when new soil is formed from parent rocks, one centimetre of soil may need hundred to thousand years to build up. Formation of 2.5 centimetre of the fertile top soil can take anything from hundred to two thousand years. Also through a constantly self-reinforcing process, the soil becomes enriched with dead organic matter some of which is called humus- the thin layer at the top, which makes the soil fertile. Humus contains all the essential macro and micro nutrients necessary for plant growth. Dead organic matter amounts to to only about one per cent of the soil by weight, but it is a vital component, acting both as a sponge (to absorb moisture) and as a source of minerals. The host of microorganisms and other soil organisms, especially earthworms, play a critical role in soil formation and in renewing and maintaining its natural fertility.

The Disappearing Soil Mantle: A Silent Crisis and Potential Threat to Civilisation

Soil and civilisation go together. History is evidence that mighty civilisation of the ancient world such as the Mohenjodaro and Harappa disappeared because people did not car for their soil. Large-scale destruction of forests led to soil erosion and desertification.

The remains of these ancient civilisations stand in a barren desert today. In the last 10000 years or more, we have altered our landscape and soil structures markedly in the wake of material development (agriculture, industry, transport and urban development). Some 75 billion tonnes of topsoil (the fertile layer) are eroded away every year being washed away (by storms) into the sea or carried away with wind. Human activities (anthropogenic factors) have aggravated the problem. In some regions of the world, soil has become very fragile. It is estimated that some 6 billion tonnes of soil are eroded from India’s cropland every year. Soil erosion means less food and fibre, less forest and fuel for the future, and in short, less wealth for the planet. It also means poverty and hunger-conflicts and violence, starvation and death. Soil erosion is a ‘silent crisis’. It is a creeping death for humanity in its totality.

Nature has protected the soil by putting a green vegetal cover over it. The roots of green plants work as soil binders. Reforesting the Earth with trees and bushes, especially the native species, is the best remedial measure. Through leaf fall and retention of moisture underground, the green plants promote the population of soil microorganisms and the earthworms (the great soil makers) in soil and help in total regeneration rates can be enhances several times. In areas with highly eroded or degraded soil mantle, if proper mulching is made with organic matter (even organic wastes) and earthworm culture (from vermiculture) is added to it, soil regenerates faster and fertility is restored.

Earthworms: The Great Soil Makers

The presence of earthworms in the soil is a bio-indicator of healthy and fertile soil. One acre of fertile land may contain more than 50000 earthworms of diverse species. Earthworms are biological natural agents that affect soil regeneration, fragmentation, aeration and bring about soil turn and dispersion. Earthworm activity is so prolific that, on an average, this population ingests tonnes of organic matter; leading to upturning of tonnes of soil and world over at this rate it may mean a two-inch humus layer over the globe.

Darwin called the Earthworm as ‘Natural ploughman’ and ‘farmer’s friend’ working day and night for the farmer. They are continually ploughing and manuring the soil in the farmland. The habitat of burrowing and swallowing earth below the surfaces increase the fertility of the soil in many ways.

Interest in vermiculture technology for soil regeneration grew in recent times and several scientists have studied the impact of earthworms on degraded soils. Earthworms harbour millions of nitrogen fixing bacteria in their gut. They help in renewing the soil fertility and in soil regeneration, and also secrete valuable growth promoting substances for crop plants.

Absorbent Plastic Technology to Improve Soil Quality

The National Chemical Laboratory (NCL), Pune, has developed a super-absorbent polymer named “Jalshakti” which can absorb 250 to 500 times its own weight of water. This super absorbent plastic has a major application in soil amelioration. When mixed with soil, sand or any synthetic growing medium, the absorbent plastic increases both its water retention capacity and aeration for plant roots, thus not only improving the soil quality but also reducing the water for irrigation and saving massive water losses.